1. Field of the Invention
This invention relates to an indicator to teach the desirable receiving direction of a satellite radio wave receiving antenna while the direction of the antenna is adjusted.
2. Description of the Prior Art
When a satellite radio wave received by an antenna is demodulated and the demodulated output of the wave exceeds a predetermined reference level, an indicator lights, and when the demodulated output does not exceed the level, the indicator is extinguished. Let it be supposed that this reference level is set to a value appropriate for an area where the received level of the satellite radio wave is high, for example, for Nagoyo (the central area of Japan). When the antenna is directed in a desirable receiving direction, that is, in the direction of high received radio wave level, the indicator lights and it is otherwise extinguished. The antenna is thus mounted successfully so that it may be directed in the desirable direction.
When the indicator with the same reference level is used in an area where the received radio wave level is low, for example, in Okinawa (the south end area of Japan), the demodulated output in any receiving direction, however, does not exceed the reference level and the indicator continues to be extinguished. The indicator, therefor, is not helpful for finding the desirable receiving direction. If the reference level is lowered and the indicator operates satisfactorily in the area of low received radio wave level, this indicator, in turn, continues to light in the area of high received radio wave level and again is not helpful for finding the desirable receiving direction.
The received level of the satellite radio wave, moreover, decreases with increasing cloudiness. The reference level of the indicator is usually set to a value appropriate for the clear sky in an area. When this indicator is used under the cloudy sky even in the same area, the indicator does not light for any receiving direction and may not be helpful for determining the desirable receiving direction.